Search if all string in .txt

I am trying to run a program to look at a .txt file and if, else depending on the content

I thought would be

Searhterms = [A, B]
with('output.txt') as f:

    if ('A' and 'B') in f.read():
        print('mix')
    eLif ('A') in f.read:
        if ('B') not in f.read:
            print('ONLY A')
    elif ('B') in f.read():
        if ('A') not in f.read:
            print('ONLY B') 
    else:
        if ('A' and 'B') not in f.read:
            print('NO AB)

But if A and B present it works, but if only one it skips to the else. I am getting more confused about the longer I look at this.